Classifications

• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08G—MACROMOLECULAR COMPOUNDS OBTAINED OTHERWISE THAN BY REACTIONS ONLY INVOLVING UNSATURATED CARBON-TO-CARBON BONDS
  • C08G63/00—Macromolecular compounds obtained by reactions forming a carboxylic ester link in the main chain of the macromolecule
  • C08G63/88—Post-polymerisation treatment
  • C08G63/89—Recovery of the polymer
• • C—CHEMISTRY; METALLURGY
  • C08—ORGANIC MACROMOLECULAR COMPOUNDS; THEIR PREPARATION OR CHEMICAL WORKING-UP; COMPOSITIONS BASED THEREON
  • C08J—WORKING-UP; GENERAL PROCESSES OF COMPOUNDING; AFTER-TREATMENT NOT COVERED BY SUBCLASSES C08B, C08C, C08F, C08G or C08H
  • C08J3/00—Processes of treating or compounding macromolecular substances
  • C08J3/12—Powdering or granulating
  • C08J3/16—Powdering or granulating by coagulating dispersions

Definitions

• This invention relates to a process of recovering polymeric beads from an aqueous slurry thereof, as a soft, friable cake.
• it is concerned with the recovery of an essentially stabiliser-free cake from a slurry containing a poly(vinyl alcohol) dispersion stabiliser.
• polymeric beads for example spheroidal granules of synthetic polymer with a diameter of from 1-50 ,um, as matting and opacifying agents in products such as paint, plastics and paper.
• One particularly useful class of bead is that made from unsaturated polyester resin, which is cured by cross-linking it with styrene or a similar unsaturated monomer.
• the beads may be solid or vesi- culated and typical examples are described in, for example, Australian patent specification Nos. 434,658 and 439,432.
• Beads of this type are commonly made by a process which yields a slurry of polymer beads in water containing a poly(vinyl alcohol) dispersion stabiliser and are described in, for example, Austalian patent specification No. 445,277.
• the slurries typically have a bead content of the order of 30% by weight.
• polymer beads When such polymer beads are to be used in an aqueous product, for example in a latex paint, they can often be blended directly with the other components as an aqueous slurry, without any intermediate de-watering process. However, if the end product is to be essentially anhydrous the requirement to first de-water beads which have been made as an aqueous slurry, can raise serious economic and technical problems.
• the energy required to dry a 30% by weight slurry of beads in water by direct evaporation in an acceptable time can add an intolerable cost penalty to the beads.
• heating a bead slurry to evaporate the water can cause hard aggregates of beads to form. These aggregates may be difficult, if not impossible, to break up satisfactorily in subsequent dispersion processes. This problem appears to result from the presence in the slurry of the poly(vinyl alcohol) dispersion stabiliser.
• the present invention relates to a process of dewatering an aqueous slurry of polymer beads which slurry contains a poly(vinyl alcohol) dispersion stabiliser, characterised in that:
• the destabilising process we now disclose involves precipitating in the slurry a selected destabiliser, which causes the polymer beads to flocculate and also enables the poly(vinyl alcohol) stabiliser to be flushed from them with the effluent liquid, when de-watering is carried out.
• the slurry can then be de-watered by conventional physical means, for example by filtration or by centrifuging, to yield a soft, essentially stabiliser-free cake of polymer beads together with some residual water. If required, this cake can then be dried, for example by circulating heated air at a temperature lower than the softening point of the polymer beads, over and through the cake.
• the destabiliser shall be precipitated in the slurry, that the destabiliser itself must be insoluble in the aqueous phase thereof and that it can be produced in situ from a soluble parent compound.
• destabilisers are organic materials which may, but need not be, polymeric. They must, however, have a molecular weight of at least 200.
• the destabilisers comprise solubilising ionizable groups, the elimination of which renders the molecule as a whole insoluble in the aqueous phase of the slurry.
• the destabiliser may be, for example, a carboxylic acid.
• Suitable carboxylic acids are, for example, stearic, 12-hydroxy stearic, abietic, oleic and dimerised fatty acids, styrene/maleic anhydride copolymer, di-isobutylene/maleic anhydride copolymer and poly(acrylic acid).
• the carboxylic acid should preferably have an acid value of at least 100 mgm KOH per gm.
• Other satisfactory destabilisers are the heavy metal salts of such fatty acids.
• the destabiliser may comprise an acid grouping other than a carboxyl group.
• the distabiliser may comprise a moiety derived from sulphuric or phosphoric acids. That it, the destabiliser may be, for example, a sulphonated polystyrene or sulphated castor oil.
• Another useful class of destabiliser may comprise a moiety derived from sulphuric or phosphoric acids. That is, the destabiliser alcohol copolymer, to give a polymeric product which is alkali soluble but becomes water-insoluble when acidified.
• a somewhat similar class of destabiliser may be prepared by reacting a polymer or copolymer of methacrylate with sulphuric or phosphoric acids.
• the insoluble destabiliser may be an amine.
• the amine must be perse insoluble in the aqueous phase of the bead slurry and provided this requirement is met, the amine may be a mono-amine or a polyamine.
• the amine may, for example, be a primary amine of the structure R-NH 2 in which R is an alkyl group with a carbon chain length of 12-18 atoms.
• the carbon chain may be a fatty acid moiety derived from, for example, lauric, myristic, stearic and oleic acids and mixtures of such acids as they are derived from natural products. Suitable destabilisers of this type are tallow, coconut and soya amines.
• the amine destabiliser may be a secondary amine of the structure R-NH-R where R is an alkyl group of the type discussed hereinabove.
• the molecule may comprise both primary and secondary amine groups.
• the amine may also be a diamine with the general structure R-NH-R.1-NH ⁇ [ where R and R J are alkyl groups. Suitable compounds of this type are, for example, oleyl propylene and lauryl propylene diamine. Alternatively, it may be a fatty acid salt, for example a mono- or dioleyl salt, of such a diamine. We have found the mono-fatty acid salt of e.g. oleyl propylene diamine to be a particularly useful destabiliser for some bead slurries.
• the amine may be a zwitterion, for example if can be a compound of the structure in which R is an alkyl group, e.g. a lauryl chain.
• the destabiliser is introduced into the slurry as a soluble derivative will naturally depend on the composition of the destabiliser itself.
• an acid destabiliser may be converted to its water-soluble sodium, or potassium salt by reaction with the corresponding base and reprecipitated when required by acidifying the slurry.
• a suitable soluble acid may be reacted with e.g., barium chloride and calcium nitrate, to precipitate a corresponding metal salt of the acid.
• a convenient way of forming an amine destabiliser in the slurry is to start with a corresponding soluble alkyl acid salt and to form the insoluble destabiliser from this by an exchange reaction with e.g. a fatty acid soap of an alkali metal.
• a fatty acid soap of an alkali metal e.g. a fatty acid soap of an alkali metal.
• the soluble oleyl propylene diamine diacetate will react with sodium stearate to precipitate the corresponding insoluble stearyl destabiliser.
• the amine When the amine is a zwitterion, it may as with the acid destabilisers described hereinabove, be solubilised by converting it to an alkali metal salt by the reaction of, for example sodium hydroxide, with the carboxyl group. The destabiliser is then formed in situ in a slurry in which the salt is dissolved by acidifying the aqueous phase thereof.
• a destabilising agent it is, of course, necessary to select a material which will not react unfavourably with any component of the slurry to be treated. For example, we have observed that if the slurry contains traces of benzoic acid, e.g. as residues of benzoyl peroxide polymerisation initiator formed during bead manufacture, these can react with aliphatic amines, which would therefore be an unsatisfactory destabilising agent to use with that particular slurry.
• the quantity of destabilising material to be used depends on factors such as, for example, the concentration of poly(vinyl alcohol) in the slurry and the chemical nature and particle size of the polymer beads. It is therefore usually desirable to determine experimentally for any particular combination of slurry and destabilising material what the optimum concentration is. As a general guide, however, we have found that a concentration of 1-3% by weight based on the disperse phase content of the slurry is usually sufficient. At lower concentrations, the rate of de-watering is inhibited by incomplete bead flocculation and usually nothing is to be gained by using much higher concentrations.
• the destabilised slurry If the destabilised slurry is not already at that temperature, it must be heated to at least 50°C to complete the process, before it is concentrated by filtration or centrifuging.
• the final cake can be readily washed with water to remove remaining traces of poly(vinyl alcohol) stabiliser.
• the solids content of the final cake is typically 60-70% by weight, not allowing for any water which may be present as an internal occlusion in the disperse particles.
• the soft cake from the dewatering process can be dried by conventional means.
• the slurry of polyester beads used in this example had the following characteristics.
• the beads consisted of an unsaturated polyester resin cured by reacting it with 40% by weight of styrene monomer.
• the slurry contained 38.9% by weight of beads with a maximum diameter of 50,um and a mean diameter of 20-25 ⁇ m dispersed in an aqueous phase comprising 2.4% of poly(vinyl alcohol) based on the weight of beads present.
• the grade of poly(vinyl alcohol) used was an 88% hydrolysed poly-(vinyl acetate) which had a viscosity of 40 cps at 20°C as a 4% by weight solution in water.
• a solution of a soluble ionizable salt of a polycarboxylic acid was prepared by dissolving in water made alkaline with ammonia, 33% by weight of a copolymer of styrene and maleic anhydride in the approximate molar ratios of 52:48. The molecular weight of the copolymer wxas approximately 2500.
• the batch filtered readily through a conventional vaccum filter.
• the filter cake was water-washed to give a clean, friable product.
• the initial filtrate was noticeably viscous and gelled on addition of sodium borate, in the manner characteristic of a poly(vinyl alcohol) solution.
• a sample of the untreated slurry showed no flocculation under the microscope. Attempts to filter it through the same vacuum filter used for the destabilised slurry were unsuccessful, even when the sample was heated to 70°C and diluted with additional water.
• Example 1 The general process of Example 1 was repeated, except for the substitution of 600 parts of a 5% by weight solution of sodium stearate in hot water for the 30 parts of ionizable salt solution of that example.;
• Example 2 The batch was then heated to 70°C and filtered as described in Example 1. Good filtration rates were again obtained. The washed filter cake was soft and friable. Poly(vinyl alcohol) was again observed in the filtrate.
• a sample of 2604 parts of polyester beads slurry adjusted to a pH of 7.5-8.5 was prepared as described in Example 1.
• the molecule comprises both primary and secondary amine groups.
• a sample of 2604 parts of polyester beads slurry adjusted to a pH of 7.5-8.5 was prepared as described in Example 1.
• the polyester beads were highly flocculated.
• Example 1 Similar favourable results to that of Example 1 were obtained when the slurry was filtered as described in that example.
• the filter cakes were allowed to dry in a current of warm air at 70°C to yield free-flowing powders essentially free of any agglomerates of beads.
• the beads used in this example were similar to those of Example 1 but the beads content was 37% by weight of the slurry.
• the batch was then subjected to filtering trials by the general method of Example 1, but using a series of processing temperatures which did not exceed that at which the poly(vinyl alcohol) precipitates from aqueous solution.
• the time taken to filter equal parts of slurry at the different temperatures and the appearance of the filtrate is shown in the following table.
• the materials selected were products sold under the Trade Mark "Alfloc" as flocculants for use in industrial water clarification processes.
• the particular grades used had the following characteristics: Each flocculant was made up into an aqueous solution and added to a sample of slurry as used in Example 1, at the concentration recommended by the manufacturer. In each case, flocculation of the beads was observed under the microscope, but filtration rates were extremely slow and the filtrate was quite cloudy. The appearance of the filter cake was consistent with it having retained a substantial proportion of the poly(vinyl alcohol) slurry stabiliser.
• destabiliser comprising sulphuric acid moieties.
• a slurry of 40% by weight 35,um mean diameter cross-linked polyester beads in an aqueous phase comprising 2.5% by weight of poly(vinyl alcohol) stabiliser was destabilised in the following manner.
• Acetic acid was then added, with stirring, until the pH reached 3.2.
• a sample of slurry examined by microscope showed that the beads, previously well dispersed, had become highly flocculated.
• the destabilised slurry filtered readily on a vacuum filter.
• the filtrate contained poly(vinyl alcohol).

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• Chemical & Material Sciences (AREA)
• Health & Medical Sciences (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Medicinal Chemistry (AREA)
• Polymers & Plastics (AREA)
• Organic Chemistry (AREA)
• Dispersion Chemistry (AREA)
• Processes Of Treating Macromolecular Substances (AREA)
• Addition Polymer Or Copolymer, Post-Treatments, Or Chemical Modifications (AREA)
• Polymerisation Methods In General (AREA)
• Separation Of Suspended Particles By Flocculating Agents (AREA)

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• 1978
  • 1978-07-03 IE IE1335/78A patent/IE47018B1/en unknown
  • 1978-07-03 NZ NZ187768A patent/NZ187768A/xx unknown
  • 1978-07-05 US US05/922,050 patent/US4154923A/en not_active Expired - Lifetime
  • 1978-07-12 AR AR272932A patent/AR221702A1/es active
  • 1978-07-14 AT AT0510178A patent/AT369763B/de not_active IP Right Cessation
  • 1978-07-14 CA CA307,411A patent/CA1094701A/en not_active Expired
  • 1978-07-14 ZA ZA784011A patent/ZA784011B/xx unknown
  • 1978-07-14 EP EP78100403A patent/EP0000524B1/en not_active Expired
  • 1978-07-14 DE DE7878100403T patent/DE2862039D1/de not_active Expired
  • 1978-07-17 MX MX174204A patent/MX150093A/es unknown
  • 1978-07-17 PT PT68310A patent/PT68310A/pt unknown
  • 1978-07-17 BR BR7804583A patent/BR7804583A/pt unknown
  • 1978-07-18 FI FI782268A patent/FI63426C/fi not_active IP Right Cessation
  • 1978-07-18 IT IT25835/78A patent/IT1097865B/it active
  • 1978-07-18 NO NO782479A patent/NO149816C/no unknown
  • 1978-07-19 JP JP8721878A patent/JPS5448882A/ja active Pending
  • 1978-07-19 ES ES471865A patent/ES471865A1/es not_active Expired
  • 1978-07-19 DK DK323778A patent/DK323778A/da not_active Application Discontinuation

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